Life　cycle　inventory　(LCI)　can　be　used　to　quantify　the　energy　input,　material　assumption　and　environmental　emission　of　a　product　system　in　their　whole　life　cycle,　and　identify　measures　to　improve　their　environmental　property.　A　data　flow　balancing　algorithm　was　built　by　the　definitude　of　LCI　steps　and　the　flow　sheet　modeling,　and　LCI　data　compiling　method　was　also　gained　based　on　the　recursion　algorithm　for　the　unit　process　data　flow.　Furthermore,　the　built　LCI　algorithm　was　used　to　verify　and　practise　life　cycle　inventory　of　iron　and　steel　production.